Apparatus for the liquid-phase epitaxial growth of multi-layer wafers

ABSTRACT

An apparatus for the liquid-phase epitaxial growth of multilayer wafer comprising a refractory furnace tube, a boat placed in the furnace tube and having a plurality of bathes which are aligned in the longitudinal direction of the furnace tube and respectively carry solutions each containing semiconductive substances, and a holding member for holding a substrate which is arranged to succeedingly flood the substrate with the solutions so as to epitaxially grow a multi-layer wafer on the substrate. The holding member arranged to upset the substrate upon pickingup or separating of the substrate from the solution so that the solution remained on the substrate is dropped from the substrate whereby unwanted mixing of the solutions neighbouring each other can be avoided.

United States Patent 1 91 Kobayasi et al.

[ Jan. 8, 1974 [75] Inventors: l-liroyuki Kobayasi; lsamu Akasaki,

both of Osaka, Japan [73] Assignee: Matsushita Electric IndustrialCompany, Limited, Osaka, Japan [22] Filed: Mar. 1, 1972 [21] Appl. No.:230,661

[30] Foreign Application Priority Data Mar. 5, 1971 Japan 46/12067 [52]US. Cl. 118/422, 23/273 SP, 148/1.5, 148/172 [51] Int. C1. B056! 3/00,BOld 9/00 [58] Field of Search 118/58, 415, 421,

118/422, 423, 426, 429; 148/15, 171, 172; 23/273 SP, 301 SP [56]References Cited UNITED STATES PATENTS 3,565,702 2/1971 Nelson 148/1723,665,888 5/1972 Bergh et a1. 118/58 3,677,228 7/1972 Panish et a1. 118/422 3,697,330 10/1972 Minden et a1. 23/273 SP 3,705,825 12/1972Touchy et al 148/15 Primary Examiner-Louis K. Rimrodt [5 7] ABSTRACT Anapparatus for the liquid-phase epitaxial growth of multi-layer wafercomprising a refractory furnace tube, a boat placed in the furnace tubeand having a plurality of bathes which are aligned in the longitudinaldirection of the furnace tube and respectively carry solutions eachcontaining semiconductive substances, and a holding member for holding asubstrate which is arranged to succeedingly flood the substrate with thesolutions so as to epitaxially grow a multilayer wafer on the substrate.The holding member arranged to upset the substrate upon picking-up orseparating of the substrate from the solution so that the solutionremained on the substrate is dropped from the substrate whereby unwantedmixing of the solutions neighbouring each other can be avoided.

I 1 Claim, 9 Drawing Figures PAIENTEDJAN 81914 I 3.783.825

sum 1 or 3 Fig. PRIOR ART minim m Bum 3.783.825

SHEET 2 OF 3 APPARATUS FOR THE LIQUID-PHASE EPITAXIAL GROWTH orMULTI-LAYER WAFERS The present invention relates to apparatus for makingsemiconductor wafers, and more particularly, to an apparatus forepitaxially growing a semiconductive multi-layer wafer on a substrate.

Several apparatus for making multi-layer semiconductor wafers have beendevised, one of which is an apparatus disclosed on page 109 of theApplied Physics Letters, vol. 17, No. 3, 1970. This apparatus includes aplurality of baths carrying solutions each containing substances to formone layer of the multi-layer, and a holder for holding a substrate andfor successively dipping in the baths the substrate so as to deposit andgrow the substances on the substrate in the form of the multilayer.Since the apparatus achieves the epitaxial growth step for each of themultiple layers without exposing of the substrate to the atmosphere,unwanted pollution of the layers is avoided.

However, a problem is still encountered in that one solution carried byone of the baths is liable to unwantedly remain on the substrate and bedelivered to the succeeding bath thereby to cause it to pollute anothersolution carried in the succeeding bath.

It is accordingly an object of the present invention to provide animproved apparatus for making a multilayer wafer.

It is another object of the invention to provide an apparatus for theliquid-phase growth of a multi-layer wafer which can avoid unwantedpollution of the solution containing substances to be grown.

It is another object of vthe invention to provide an apparatus for theliquid-phase epitaxial growth of a multilayer wafer which is readilycontrolled in temperature Further objects, features and advantages ofthe invention will become apparent from a consideration of the followingdescription, the appended claims, and the accompanying drawings inwhich:

FIG. 1 is a longitudinal sectional view of a conventional apparatus;

FIG. 2 is a cross-sectional view of the FIG. 1, taken along a line 2-2;

FIG. 3 is a longitudinal sectional view of an embodiment of the presentinvention;

FIGS. 4A and 4B. are cross-sectional views taken along a line 4-4 shownin FIG. 3;

FIG. 5 is a schematic view of another embodiment of the invention;

FIG. 6 is a longitudinal sectional view of the apparatus of FIG. 5; I

FIGS. 7A and 7B are cross-sectional views taken along a line 7--7 shownin FIG. 6;

Corresponding characters of reference designate like parts in theseveral views.

Referring now to the drawings and'particularly to FIGS. 1 and 2, thereis shown an apparatus described apparatus of on page 109 of the AppliedPhysics Letters, vol. 7, No. 3, 1971, which comprises a refractoryfurnace tube made of a refractory material such as quartz. The furnacetube 20 may be heated by a heating coil (not shown) surrounding thefurnace tube 20. In the furnace tube 20 is placed a columnar boat 21which has a bore 22 extending therethrough and a plurality of, in thiscase, four bathes 23a, 23b, 23c and 23d on its upper portion. Each ofthe baths communicate with the bore The temperature in the vicinity ofthe substrate 25 is detected through the thermocouple 28. A push rod 29is connected to a side wall of the boat 21. The push rod I 29 isarranged to be movable in the longitudinal direction of the furnace tube20. The baths 23a, 23b, 23c and 23d respectively carry solutions 30a,30b, 30c and 30d each containing semiconductive substances inpreselected proportions.

In operation, the boat 21 is so positioned as to separate the substrate25 from any of the solutions 30a, 30b, 30c and 30d. The solution 30a isfirst preheated to about 800 C and, then the boat 21 is slid to the leftof the figure through the push rod 29 until the substrate 25 is floodedwith the s0luti0n30a. Thereafter, the temperature of the solution 30a islowered to about 790 C so that the semiconductive substances containedin the solution 30a precipitate and an epitaxial layer grows on thesubstrate 25. The thickness of the epitaxial layer is in accord withdegree of the cooling of the solution 30a. Upon completion of theepitaxial growth, the boat 21 is further slid through the push rod 29until the substrate 25 is flooded .with the solution 30b whilecontrolling the temperature of the solution 30b. The solution 30b isthen cooled by either several or 10 and several degrees of centigradesoas to precipi-' tate the substances in the solution, whereby anotherepitaxial layer grows on the epitaxial layer previously grown. Similarprocedures to the above-stated procedures are succeedingly repeated soas to produce a multi-layer wafer on the substrate 25.

The above-mentioned apparatus is capable of making a multi-layer waferwith-a plurality of epitaxial layers each having a desired thickness bycontrolling the, temperature of the substrate and the solution.Furthermore, since all the steps for making the multi-layer wafer areperformed without exposing the substrate to the atmosphere, unwantedpollution of the epitaxial layers is avoided. It'is, however, a problemthat a small amount of solution remains on the epitaxial layer after thecompletion of the growth of the epitaxial layer. The solution remainedon the epitaxial layer is unwantedly delivered to the succeeding bathand mixed with the solution in the succeeding bath, whereby the solutionis polluted or proportions of the contents of the solution is changed.In order to avoid this problem, an improved apparatus for the epitaxialgrowth of a multi-layer wafer is provided by the present invention. 7

In FIGS. 3, 4a and 4b, a preferred embodiment of the invention isillustrated, comprising a refractory furnace tube 40 made of arefractory material such as-quartz. The furnace tube 40 is heated by aheater such as heating coil (not shown) and arranged rotatable about itscentral axis. In the furnace tube 40 is placed a cylindrical boat 41which may be made of graphite and may be formed into another form, ifdesired. The boat 41 is provided on its peripheral wall with a groove 42extending in the longitudinal direction of the boat 41. A claw member 43is inserted into the groove 42, the claw member 43 being secured to thefurnace tube 40 so that the boat 41 is fixed to the furnace tube 40 inthe circumferential direction of the tube 40 but slidable in thelongitudinal direction. The boat 41 is provided with a bore 44 extendingtherethrough in the longitudinal direction and having, in this case, arectangular section. The boat 41 has two baths 45a and 45b whichcommunicate with the bore 44 and respectively carry solutions 46a and46b each containing semiconductive substances in preselectedproportions. If desired, the boat 41 may have other baths. The boat 41has another bore 47 extending parallel to the bore 44. Into the bore 44is snugly and slidably inserted a columnar holding member 48 which holdsa substrate 50 in its recess portion 51 formed to face the baths 45. Thesubstrate 50 is secured to the recess portion by means of a clampingmember 52. A stopper 53 prevents the holding member 48 from moving tothe left of this figure. A thermocouple 54 is inserted into the bore 47of the boat 41 to detect the temperature in the vicinity of thesubstrate 50. A push rod 55 is connected to one side wall of the boat 41to move the boat 41 to the left. In operation, the boat is first sopositioned that the substrate 50 faces and overlie the bath 45a carryingthe solution 46a as shown in FIGS. 3 and 4. The substrate may bepositioned against the utmost left end of the boat 41, when thesubstances in the solution 46a will evaporate at a relatively lowtemperature. The furnace tube 40 is then heated by the heater so as topreheat the solution 46a and the substrate 52 to a predeterminedtemperature. Thereafter, the furnace tube 40 together with the boat 41are rotated through 180 about the central axis of the furnace tube 40 asshown in FIG. 48.

Being apparent from the FIG. 4B, the substrate 50 is flooded with thesolution 46a. The temperature of the furnace tube 40 is reduced so as tocool the solution 460 whereby the substances dissolved in the solution46a precipitate to deposit and grow on the substrate 50 in the form of afirst epitaxial layer. When the thickness of the first epitaxial layerreaches a predetermined value the furnace tube 40 is rotated through 180about the central axis so as to permit the boat 41 to be restored to aposition as shown in FIG. 4A whereby the substrate 50 is separated fromthe solution 46a. Then, the boat 41 is slid to the right by the push rod55, while controlling the temperature of the solution and the substrate50, until the substrate faces and overlies the bath 45b carrying thesolution 46b. The furnace tube 40 is then rotated through l80 about itscentral axis so that the boat 41 is rotated and the substrate 50 and thefirst epitaxial layer are flooded with the solution 461;. Thetemperature of the furnace tube 40 is then reduced to permit thesubstances contained in the solution 46b precipitate to deposit and growon the first epitaxial layer in the form of a second epitaxial layer.Upon completion of the growth of the second epitaxial layer, the furnacetube 40 is rotated through 180 about the central axis to separate thesubstrate 50 from the solution 46b. A desired number of baths may beprovided and the same procedure as the above described may be repeatedso as to succeedingly grow epitaxial layers overlying one another in theform of a multilayer wafer.

In this instance, it is to be noted that the cylindrical boat 41 may bearranged to be slidable on the inner peripheral wall of the furnace tube40 in the circumferential direction of the furnace tube 40, if desired,by omitting the claw member 43.

It is now apparent from the above description that when the boat 41 isslid to permit the substrate to face and overlie the succeedingsolution, the substrate 50 and the recess portion 51 are upset with theresult that the solution contacted with the substrate 50 during theepitaxial growth is completely dropped from the substrate 50 whereby theunwanted'mixing between the solutions neighbouring each other can beavoided.

Referring now to FIG. 5, there is shown a main portion of anotherembodiment of the present invention, which comprises a boat 41 havingtwo baths 45a and 45b each carrying a solution containing semiconductivesubstances. On shoulder portions of the boat 41 opposite to each otherstand pair of journal members and 60 each of which has a bore in itscentral portion. A columnar holding member 48 is journaled on thejournal members 60 and 60. The holding member 48 has a projection 51having a top end for carrying a substrate 50 on which a multi-layerwafer is to be grown. The projection 51 should have such a large heightthat the end portion thereof passes through the bath 45a or 45b when theholding member is rotated through one rotation.

The above-described arrangement is positioned in a refractory furnacetube 40 as shown in FIG. 6.

In operation, the holding member 48 first so positioned as to separatethe substrate 50 from the solution 46a as shown in FIG. 7A. The furnacetube 40 is then heated by the heater so as to preheat the solution 460and the substrate 50 to a predetermined temperature. Thereafter, theholding member 48 is rotated so as to dip the substance 50 into thesolution 46a as shown in FIG. 7B. The temperature of the furnace tube 40is reduced so as to cool the solution 46a whereby the substancesdissolved in the solution 460 precipitate to deposit and grow on thesubstrate in the form of an epitaxial layer. When the thickness of theepitaxial layer reaches a predetermined value, the holding member 48 isrotated so as to place the substrate in the initial position. Then, theholding member 48 is slided on the bore of the journal members-60 and 60until the substrate 50 overlies the succeeding solution 46b, while thetemperatures of the solution 46b and the substrate 50 are controlled.The holding member 48 is again rotated about its central axis so as todip the substrate 50 and the previously grown epitaxial layer into thesolution 46b. The temperature of the solution 46a is then reducedthereby to cause the substances contained in the solution 46b toprecipitate to deposit and grow on the previously grown epitaxial layer.Upon completion of the growth of the following epitaxial layer, theholding member 48 is rotated so as to separate the substance 50 from thesolution 46b. A desired number of baths maybe, of course, provided andthe same procedure as the above-described is repeated thereby tosucceedingly grow a desired number of epitaxial layers overlying oneanother in the form of a multi-layer.

By using the apparatus shown in FIGS. 3, 4A and 43, several method ofmaking a multi-layer wafer were performed as described in the followingexamples:

EXAMPLE I A plate of n-GaAs crystalline was used as the substrate 50.The solution 46a included a certain amount of gallium as a solvent, andgallium arsenide of such an amount that a desired amount of galliumarsenide precipitate by reducing the temperature of the solution.

The solution 46a further included aluminium of 0.15 percent by weight ofthe solvent of gallium and a small amount of silicon as impurities. Thesolution 46b included gallium as a solvent, and gallium arenide of suchan amount that a desired amount of gallium arsenide precipitate throughreducing the temperature of the solution 46b. The solution 46b furtherincluded aluminium of 0.3 percent by weight of the solvent of galliumand a small amount of silicon as impurities. Before dipping thesubstrate 50 into the solution 46a, the substrate 50 and the solution46a were preheated to about 860 C. The furnace tube 40 was then rotatedso as to contact the substrate 50 with the solution 46a, and thesolution 46a and the substrate 50 were first cooled through a rateC/minute and further cooled through another rate of 2 C/minute therebyto grow a first epitaxial layer of GaAlAs crystal with Si impurity. Thefirst epitaxial layer therefore had a region of p-type and anotherregion of n-type through the behavior of the silicon impurity. Uponcompletion of the abovedescribed growth of the first epitaxial layer,the furnace tube 40 was rotated so as to separate the substrate 50 fromthe solution 46a and slid in a direction of the central axis of thefurnace tube 40 so as to permit the substrate 50 to face and overlie thesolution 46b. The same procedure as for the first epitaxial layer wasrepeated so as to produce a second epitaxial layer on the firstepitaxial layer of GaAlAs crystal. The second epitaxial layer also hadp-type and n-type regions. The first epitaxial layer of GaAlAs crystalincluded AlAs component in percent of mol fraction and the secondepitaxial layer of GaAlAs included the AlAs component in 50 percent ofmol fraction. Furthermore, the second epitaxial layer has a widerforbidden band than the first epitaxial layer so that light raysproduced in the forbidden band in the first epitaxial layer may bemostly radiated without being absorbed in the second layer when themulti-layer wafer is utilized for a luminous element.

EXAMPLE ll A plate of n-type GaP crystal with a large amount of latticedefects was used as the substrate 50. The solution 46a contained asolvent of gallium and a solute of gallium phosphide of such an amountthat a desired amount of gallium phosphide precipitate through reducingthe temperature of the solution 46a. The solution 46a further containedtellurium of 0.01 mol percent of the solvent as an impurity. Thesolution 46b contained a solvent of gallium phosphide, a solute ofgallium of the same amount as the solution 46a, and a zinc of 0.02 molpercent of the solvent as an impurity.

The above-mentioned arrangement similarly operated except that thesolution and the substrate were preheated to about l,000 C and cooled ata rate of 1 1 C/min. As a result, a wafer was obtained, which includes afirst epitaxially layer of n-Gap and a second epitaxial layer of p-GaP.A p-n junction was formed between the first and second layers. The p-njunction radiates a green or yellow light ray when exited by electricenergy.

EXAMPLE 1]] The boat 41 had, in this case, three baths. A plate ofgallium arsenide was used for the substrate 50. First and thirdsolutions respectively contained a solvent of gallium and a solute ofgallium arsenide of such an amount as to saturate the solution at about850 C. The

solutions further contained aluminium of 0.02 percent by weight of thesolvent and a trace of impurity of zinc and tin. A second solutioncontained a solvent galliumand a solute of gallium arsenide of such anyamount as to saturate the solution at about 850 C. The second solutionfurther contained a trace of an impurity of silicon.

The above-described arrangement was operated in a manner similar toExample ll. The resultant wafer radiated laser-ray having spectrum witha peak at 1.45 eV when the wafer was used for a Fabry-Perot typesemiconductive laser.

EXAMPLE lV Even if the surface of the substrate is contaminated orcontains a lot of defects or impurities, a preferred semiconductivewafer was obtained through the following procedure.

A first solution contained a solvent, a solute of the same substance asone constituting the substrate. The amount of the solute was selected soas not to saturate the first solution when the first solution waspreheated. Thus, the substance in the surface of the substrate wasdissolved until the substance saturate the first solution so that thesurface was cleared, when the substrate was dipped into the solution.Thereafter, the same procedure as the preceding Examples was repeated soas to produce a plurality of epitaxial layers on the thus cleanedsurface of the substrate.

It is apparent from the foregoing description and Examples that theapparatus of the present invention is capable of avoiding an unwantedmixing between the source solutions neighboring each other through therotation of the holding member to upset the substrate so as to removethe solution remained on the substrate before the succeeding step. 7

Furthermore, since the apparatus grows a plurality of epitaxial layerson a substrate without exposing the substrate to the atmosphere,unwanted pollution of the surface of the substrate can be avoided. lnaddition, since the whole steps for the apparatus are achieved bycontrolling only one furnace tube, the temperature controlling of thesolution and the substrate and-the thickness controlling of theepitaxial layer is readily performed.

The apparatus for the epitaxial growth of multi-layer wafers describedabove are understood illustrative apparatus only and that the inventionis not to be limited to the specific construction and arrangement shown.

What is claimed is:.

1. An apparatus for depositing on a substrate successive epitaxiallayers of crystalline semiconductive material from the liquid phase,which comprises;

a refractory furnace tube horizontally arranged;

heating means associated'with said tube;

a boat disposed in said furnace tube with the longitudinal axis of said,boat extending approximately parallel to the longitudinal axis of saidtube;

means defining, on an upper surface of said boat, at least two cavitiesconfining therein separate baths of said semiconductive material inmolten solutions, said cavitiesbeing aligned in a direction parallel tothe central longitudinal axis of said furnace tube;

support plates provided at the opposite ends of said boat and extendingupwardly from the upper surface of the boat and embracing said cavitiestherebetween;

means defining a bore in each of said support plates,

said bores being in alignment; and

a columnar holding member rotatably slidably 8 movement of said holdingmember and being alignable with said cavities, said projection extendingoutward from said holding members a sufficient distance so that whensaid holding member is rosubstrate can be brought into contact with asolution in a cavity with which said projection is aligned'andsubsequently can be moved out of contact with that solution. 7

1. An apparatus for depositing on a substrate successive epitaxiallayers of crystalline semiconductive material from the liquid phase,which comprises; a refractory furnace tube horizontally arranged;heating means associated with said tube; a boat disposed in said furnacetube with the longitudinal axis of said boat extending approximatelyparallel to the longitudinal axis of said tube; means defining, on anupper surface of said boat, at least two cavities confining thereinseparate baths of said semiconductive material in molten solutions, saidcavities being aligned in a direction parallel to the centrallongitudinal axis of said furnace tube; support plates provided at theopposite ends of said boat and extending upwardly from the upper surfaceof the boat and embracing said cavities therebetween; means defining abore in each of said support plates, said bores being in alignment; anda columnar holding member rotatably slidably mounted through saidaligned bores, said holding member having a projection radiallyextending therefrom, said projection having, on its end portion, saidsubstrate, said projection being disposed on said holding member at alocation where it is confined between said support plates during slidingmovement of said holding member and being alignable with said cavities,said projection extending outward from said holding members a sufficientdistance so that when said holding member is rotated at most through 360angular degrees said substrate can be brought into contact with asolution in a cavity with which said projection is aligned andsubsequently can be moved out of contact with that solution.